1. Technical Field
This application relates to computer storage devices, and more particularly to the field of migrating data between storage devices.
2. Description of Related Art
Host processor systems may store and retrieve data using a storage device containing a plurality of host interface units (host adapters), disk drives and other physical storage, and disk interface units (disk adapters). Such storage devices are provided, for example, by EMC Corporation of Hopkinton, Mass., and disclosed in U.S. Pat. No. 5,206,939 to Yanai et al., U.S. Pat. No. 5,778,394 to Galtzur et al., U.S. Pat. No. 5,845,147 to Vishlitzky et al., and U.S. Pat. No. 5,857,208 to Ofek. The host systems access the storage device through a plurality of channels provided therewith. Host systems provide data and access control information through the channels of the storage device and the storage device provides data to the host systems also through the channels. The host systems do not address the physical storage of the storage device directly, but rather, access what appears to the host systems as a plurality of logical volumes. The logical volumes may or may not correspond to the actual disk drives and/or other physical storage.
Data storage capabilities from multiple locations and multiple physical storage devices may be integrated to present the user with a somewhat unified data schema with storage resources that a user accesses transparently and somewhat independently from the actual hardware/location used for the storage. For example, a data storage cloud may appear to an end user as a single storage system even though the data may actually be stored on a number of different storage systems that may be provided in different locations and/or may use different storage hardware. The user would see a plurality of logical storage units (LUNs) but may not know (or care) about the underlying physical storage supporting the LUNs.
In some cases, the particular location used for physical storage for particular LUNs may be optimized based on one or more criteria. For example, if physical storage is provided using two separate locations, a user may manually select one of the locations any number of reasons, such as proximity to computing resources, cost, etc. Once the initial selection is made, the user may then access the LUN without regard to the underlying physical storage. Of course, automated systems may select the underlying physical storage automatically and without user intervention using some of the same or similar criteria.
However, there may be competing criteria that result in it being desirable to provide underlying physical storage at one location for some of the time while providing the underlying physical storage at one or more other locations at different times. For example, it may be desirable to provide employee records at a first location because the storage costs are relatively low, but it may be desirable to have the records at a second (different) location once a week where payroll processing is performed. The data may be moved manually by a user prior to and after each payroll processing or may be moved by an automated process that anticipates the processing at the second location each week. In either case though, all of the employee data (e.g., the entire LUN) may be moved from the first to the second location (and back) even if only a small portion of it is needed each week for payroll processing.
Accordingly, it is desirable to provide a system that avoids having to move/locate large portions of data when it is optimal to move only small portions.